Conventionally, swash plate compressors are used in automotive air conditioners and the like as a device for compressing a refrigerant gas. The swash plate compressor is composed of a cylinder block having a plurality of cylinder bores disposed in a direction parallel to an axial center, a swash plate held on a drive shaft in the cylinder block so as to rotate integrally with the drive shaft, pistons sidably inserted in the cylinder bores, and shoes for reciprocatively moving the pistons by the rotation of the swash plate.
Generally, a large load and a large slipping speed act on the sliding surfaces of the swash plate and the shoes of the swash plate compressor. In particular, the effect of the load is large when aluminum or an aluminum alloy is used as the base metal of the swash plate to reduce the weight thereof. Accordingly, consideration must be given to the lubricating ability under severe sliding conditions such as when there is no lubrication at start up or when there is a high sliding load.
A soft surface coating having a low frictional resistance which is applied to one of the opposed surfaces of the swash plate and the shoes to reduce the frictional resistance of the sliding surfaces between the swash plate and the shoes is disclosed in, for example, Japanese Patent Application Laid-open No. 2-130272 and Japanese Patent Application Laid-open No. 60-22080. That is, a soft surface coating composed of only tin or tin and a metal selected from copper, nickel, zinc, lead, indium, etc. is proposed in the former publication, and a coating containing a solid lubricant such as molybdenum disulfide, tungsten disulfide, graphite, boron nitride, lead oxide, fluoro-resin, etc. is proposed in the latter publication
When a surface coating is applied, a common practice in the conventional way of thinking is to coarsen the surface of the base or substrate for the surface coating by shot blasting or the like. Specifically, a average coarseness of the substrate is made to be about 10 .mu.mRz at ten point mean roughness to increase the adhesive properties of the surface coating with the substrate so that the surface coating does not exfoliate easily.
Note that when the surface coating is directly formed on the surface of the base metal of the swash plate or the shoes, the surface of the base metal serves as the substrate referred to here. However, when a coating having a high wear resistance is applied to the surface of the base metal, as a countermeasure to the surface coating being worn, and then the soft surface coating is applied thereon, the surface of the high wear resistance coating serves as the substrate. When the base metal is composed of, for example, aluminum, it is known to apply an aluminum anode coating to the surface of the base metal as the high wear resistance coating.
However, the conventional arrangement as described above has a problem in that although excellent lubricating properties can be achieved when the soft surface coating is not worn, the life of the soft surface coating cannot be prolonged because it has low resistance to wear. Further, although a soft surface coating such as one containing molybdenum disulfide and the like is characterized in that it fluidizes as its temperature increases, it has not yet been conceived of to make use of this feature because the surface of the substrate of the soft surface coating is coarsened to increase mechanical adhesive properties between the soft surface coating and the substrate.
Accordingly an object of the present invention made in view of the problems of the prior art is to enhance the lubricating ability and wear resistance of the sliding surfaces of a swash plate and shoes and maintain them for a long period of time.